The invention relates to a method for recovering glass from old glass by the continuous feeding of the glass scrap in the outspread state onto an open, continuously running conveyor system, by manual and mechanical sorting out of nonglass impurities such as iron and nonferrous metals as well as nonmetallic contaminants, by mechanical crushing of scrap glass in a crushing apparatus and, if desired, sorting by shard size.
The product of the method, a mass of shards within a certain shard-size range, serves later as cullet for glass melting furnaces for the production of new glass products.
The recycling of glass has gained increasing importance in recent years. The collection of old glass has become common practice everywhere since it was recognized that old glass is to be considered not only as waste but chiefly also as a raw material for the production of new glass. It is a problem that nonglass components, including metal bottle caps or parts of closures and ceramic stoppers, as well as organic impurities including pieces of plastic, labels, pieces of wood, stones and foreign matter of all kinds arbitrarily thrown into the scrap glass containers. If glass scrap only of one particular color is needed, glass of different color must be considered as nonglass components which have to be removed together with the other undesirable components if it is to be at all possible to produce new glass with the desired qualities.
Glass scrap is delivered, as a rule, in the form of a mixture of widely varying sizes. The sizes of the pieces range from small fragments through larger chunks such as bottle bottoms, all the way to whole bottles. Particularly undesirable are bottles of a certain type in which a stopper consisting of ceramic is attached to the bottle neck by a steel wire clamping mechanism. The stopper parts in this case are very difficult to remove from the mixed shards.
In one known method of the kind described in the beginning the shard mixture delivered is spread out by a feeder chute onto a conveyor system in the form of a conveyor belt, and fed first to a magnetic separator and then to a visual inspection station in which personnel watch over the movement of the entire shard mixture and sort out by hand any impurities as well as glass pieces of the wrong color. This operation is not only very fatiguing and in the course of time leads to errors, but it also limits the throughput to a great degree. Furthermore, due to the different sizes of the glass pieces, impurities are carried partially covered up through the inspection station, so that they necessarily remain undetected.
In the known methods the entire mass of shards including the undiscovered impurities are fed to a breaking apparatus, a so-called "shard breaker." In the latter any unavoidably small but otherwise suitable shards are again crushed, especially on account of the presence of larger pieces of glass. Consequently, larger amounts of energy than absolutely necessary are needed for driving the shard breaker. By means of subsequent separating stations, which may be equipped with magnetic apparatus, aspirator nozzles or the like, additional impurities composed of ferrous and nonferrous metals as well as organic substances are separated out, in which case the small glass fragments and the large total amount o glass throughput prove to be a hindrance. In particular, the power of the aspirator nozzles cannot be adjusted to an optimum level because they pick up the fine glass particles.
In addition to a high specific energy consumption, the apparatus parts needed for the known process are relatively bulky. They therefore necessitate high investment and operating costs, both for the apparatus and for the corresponding complex of buildings.